


Thrill-Seeker

by StripesnBooks



Category: Undertale (Video Game)
Genre: Alternate Universe - Soulmates, Biting, Ecto-Penis (Undertale), Ecto-Tongue (Undertale), F/M, Female Reader, Multiverse, Penis In Vagina Sex, Porn With Plot, Reader-Insert, Sex, Smut, Soul Bond, Soul Sex, Vaginal Sex, tags will be updated as I go, theres gonna be some au hopping
Language: English
Status: Completed
Published: 2018-07-14
Updated: 2019-02-10
Packaged: 2019-06-10 07:56:21
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 4
Words: 8,442
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/15287148
Author URL: https://archiveofourown.org/users/StripesnBooks/pseuds/StripesnBooks
Summary: When Sans loses his soulmate, he turns to his machine to see if he can jump to another timeline and see you one last time. but... why were you missing in so many of these already?After months of trying to get underground to see the mysterious mage city, you return to your hotel room to find a monster claiming to be your soulmate, but from another dimension? Well, you feel your soul calling for him, so he's not lying about at least one part. And he claims he can get you into the mysterious mage city!





	1. Journey to The Bone Zone

A thrill seeker. That was the most common description you would get once they heard about the rollercoasters, sky-diving, bungee jumping, flying lessons… honestly, it got kind of annoying to have the rest of your personality overlooked for that, so you stopped talking about it.

 

…

 

Or at least, you told yourself you would. But it was so fun, and you wanted to talk about your experiences!

 

And so Rosalyn rolled her eyes at you as you moaned into the diner table. “I keep telling you, just embrace being labeled, or find something even more outlandish for them to label you as. You can’t escape yourself.”

 

“I’m a three dimensional person, dammit!” you responded, lifting your head just long enough to pop another fry into your mouth before purposefully slamming your forehead back onto the table. “I love the good things in life, food, adventure, animals, dessert…”

 

“Gorgeous scenery, long walks on the beach…” Rosalyn’s voice took on a teasing tone. “As long as it’s new. You’re flighty as hell.”

 

“Am not!” okay, maybe you were just a little. New things were just so fun and exciting! “Ugh i guess i should head home soon, you have that shoot in the morning, don’t you?”

 

“Yup.” she popped her ‘p’. “The action packed life of a reality television star.” Rosalyn was a popular side character in a moderately popular kid’s TV show. You had met each other when there was a crossover with your travel show, where you showcased interesting towns around the nation and the world, in an attempt to be more educational. You had almost immediately hit it off and become fast friends.

 

“Have fun. I don’t think i’ll stay in ebott much longer if they keep refusing to let me into the Underground.” you finally picked yourself up and slumped back in your seat, watching as Rosalyn pulled out the money to pay for her meal.

 

“I think you should give up on that anyway. I mean, a whole tiny nation of mages! That’s way too dangerous for my taste.” a scaly hand dropped the appropriate change plus a tip onto the table, and Rosalyn replaced her wallet into her bag. “You’re lucky we monsters sealed them away all those years ago,” she said with a wink.

 

You rolled your eyes at your dragon friend. “Yeah yeah, monsters are amazing, humans are lame. I’m still gonna make the journey to that town by the mountain. Maybe if i show up in person they’ll let me in, you know?”

 

She snorted, exhaling a little puff of smoke. “Yeah, just throw you to the mages. You really are a thrill seeker.” she laughed at your disgruntled response and waved before leaving you to finish your fries.

 

Thrill seeker. You preferred the term adventurer.

  
  
  


They had denied you entrance. In fact, there had been quite a commotion when you had come by, something about a monster getting trapped there with all the mages, and they didn’t let you past the entry tower. So now you were driving back to the hotel room you had booked in the town near the mountain. You parked and went to get takeout at the little chinese place the next block over. A walk would feel nice, anyway. But as you made your way to the nearby restaurant, you could feel something in your chest. You rubbed at the place below your neckline. Had you eaten something wrong? Or maybe there was an air bubble stuck there? You… couldn’t have a soul sickness, could you? Nah, humans didn’t easily contract those. You reached the place, ordered, and sipped on some water while you waited, hoping it would alleviate the tight feeling of discomfort. It didn’t. And to top it off, you thought you could feel someone staring at you the whole time, even as you collected your food and returned to your room.

 

The room was comfortable and spacious, because if you could afford it, why not? You ate in your king sized hotel bed, flipping through channels. You eventually fell asleep with the TV still on, a nearly-empty takeout box lying on the other side of the bed.

  
  
  


When you woke, it was the middle of the night. It was still completely dark, save for the low steady glow of the television, and from your current position you could see that the time was in the wee hours of the morning. You could hear the low murmur of the television still; had a noisy show woken you up?

 

And then with a slight turn of your head, you saw. The television wasn’t on anymore.

  
  
  


Adrenaline shot through your system and you strained your ears to hear what that low murmur was, stared straight ahead as you tried to figure out what it was behind you that projected this light. You resisted the urge to flinch, or laugh, as something stroked your hair. You finally made out what was being said.

 

“...i’m so sorry, so, so, sorry, i should have been there. stars, you’re still so beautiful. I miss you so much, paps does too, you know, and just… i’m just so sorry. paps told me not to come, that it would only make it harder but…” there was a choked sort of laughter from the voice as whoever it was continued to stroke your hair. “he’s been making ice cream lately. says as long as its sherbert it’s not too unhealthy. he only does it because he never did it before you…” the hand finally left, and the strange light dimmed, and finally went out.

 

You waited a few minutes before shifting in bed, trying to make it look as if you had just turned in your sleep in case the intruder was still there. It was. What you saw, sitting in the chair beside your bed, was a skeleton, a hand over its eye sockets as some sort of fluid flowed out. You knew of ghost monsters, ghouls, vampires, and the like, but never a skeleton monster. His clean bones shone in the dim light that made it through the curtains, and there was a comfortable warmth in your chest at the sight. Probably because it was just so beautiful, even if they did break into your room. Why weren’t you freaking out over that? They had obviously broken into your room! To do what? Watch you sleep, touch your hair, and talk to your unconscious form? That was creepy. Why weren’t you creeped out? Why did you instead want to comfort him?

 

Before you even knew what you were doing, you had stood and walked over to the skeleton. When he heard you approach, he froze. You gently laid a hand on his skull, petting him in smooth, soothing motions. After a few seconds, he began quietly sobbing, and you just kept touching him, throwing out soothing hushing coos. Why did you think it was a he? It was rude to assume someone’s gender. But for some reason, you really thought it was. And he was obviously suffering.

 

Eventually, he took your hand in his skeletal phalanges and looked up at you with small lights that glowed from impossibly dark eye sockets. It was hauntingly beautiful, and for some reason it just felt right. There was nothing right about this situation, but you just couldn’t bring yourself to question any of it as he stood and embraced you, nuzzling his skull into your neck as he breathed your name. You just hugged right back.

 

…

 

How did he know your name?

 

“Who are you?” you whispered, and he finally pulled away, rubbing the back of his skull and not quite meeting your eyes.

 

“ah, i’m sorry, i shouldn’t have… sans. The name’s sans, sans the skeleton.” he forced a chuckle, but it just petered out nervously. “i’m, uh, from another timeline, where you… um, and we’re… soulmates…? But i really shouldn’t be here, i just… really wanted to see you again and… asgore’s beard i’m making a fool of myself…” he shuffled nervously in place.

 

“I believe you.” what.

 

“what?” he sounded both reverent and disbelieving.

 

But it was true. At least… “i believe you when you said we’re soulmates.” you tapped your chest. “I can feel my soul calling for yours.” indeed, it pulsed with warmth and unfounded love at his mere presence, and all but demanded you be closer to him. You prayed to all the deities that for whatever reason he came, he wouldn’t run away.

 

He took a step, then crossed the remaining distance that separated you, pulling you into a hungry and passionate kiss. Apparently the bone around his teeth could indeed function as lips, and he used those to kiss you thoroughly and mercilessly. There were no options besides kissing him back with just as much passion and need. All the tales you’ve heard, all the accounts of your friends, it was everything they promised, the deep love and content and comfort of being near your soulmate. And you were lucky enough to have a monster soulmate! Human soulmates weren’t attuned to their souls enough to find each other without them being drawn out, but if your soulmate was a monster…

 

He began shucking his jacket, and you found yourself in a hurry to rid yourself of the pesky fabric that was keeping you from touching this monster. Soon enough, your breasts were pressed to his ribcage, the warmth of his bones feeling, for lack of a better word, perfect. You moaned as he ran his hands over your skin, and he used it to deepen the kiss, pressing a warm, glass-like tongue into your mouth and tasting ever inch. You sucked on it dutifully and he shivered, pushing you back until you fell onto the bed with him on top of you. As you wrestled your pants off he broke the kiss, instead laving his tongue on your jawline, your neck, your breasts, running languid circles around your nipples before nipping at them.

 

“stars i can’t believe… if this is a dream i never want to wake up…”

 

Your breathy laugh devolved into a moan as he bit gently at your shoulder. “Believe it, bone boy. Stars i knew soulmates were attracted to each other but i can’t say i expected it to go this fast.” when he paused in his exploration of his tongue on your body you quickly corrected yourself. “No, i’m not complaining! Please don’t stop! Just… surprised.” he seemed satisfied and kept moving, licking at your stomach, your hips, your- “aaaahhh…” you moaned when the smooth warmth of his tongue ran its course from the bottom of your labia and up to your clit.

 

“Normally it isn’t this fast,” he confessed, “but i just got here from a different universe. A universe where you… no longer exist. For all i know, this is the first and last time i’ll ever see you.”

 

Well, that was a mood killer. You leaned forward and grabbed his skull, pulling it to your face for another deep and passion filled kiss. “No. you have me now. I won’t leave you. I won’t let you leave me. Not after i finally found my soulmate.” his kiss turned hungry again and he ground his still-clothed hips against yours as you tasted yourself on his tongue. You were so damn wet and needy, and saw no reason to waste time. “Take your damn pants off, Sans.”

 

He lost all reason as the pants were done away with, and you barely caught a glimpse of one empty socket and one glowing blue before his mouth was at your neck, leaving much less gentle nip and sucks than before. He sucked at your jugular and growled, a real animalistic growl, at your needy whines and moans. That would definitely leave a mark in the morning. But it didn’t matter because he was your soulmate. Some people went their whole lives and never found theirs. And here yours found you, just showed up in your room, claiming to be from another dimension. You didn’t even care if it was true.

 

He pulled back and you felt him line up his member with your core. You looked down to see a glowing blue dick, lacking the normal details found on a human member but shaped satisfactorily. Damn, how long had it been since you got laid? With it being that thick, this was bound to sting a bit.

 

You found the thought exciting you. 

 

He was lost in himself, hilting in you with barely restrained vigor. You let out a shriek as he pumped back and forth. Fuck, he was big. After a few thrusts your body acclimated, leaving only a satisfying after burn as he pounded into you. His hands weren’t idle, they moved around your form, grabbing at your breasts and stomach and hips, never staying in one place for long as you screamed his name. He lifted your hips, and his cock began to hit your g-spot. You were so damn close… you reached down to finger your clit, and then you were over the edge, body shaking in beautiful release as you orgasmed. He shifted your legs to lie on his shoulders and his movements became jerky and stuttered as he picked up speed.

 

You were so lost in the afterglow as he worked towards his own peak that you almost missed your soul rise from your chest and his exiting his own. He leaned down and bit at the shoulder opposite to where he marked before, sinking his teeth in deep. Before you could think straight or say anything, they circled each other and merged, just as Sans roared and came with a final slam that you swear stretched your cervix. You screamed too as you felt him, his very being merging with yours, his teeth pushing into your shoulder and you felt him taste your blood, felt his joy as your souls merged and then horror as he realized he had violated that boundary without your permission, but he couldn’t stop, and you could stop, as you both clutched each other and rode out that wave of bliss.

 

Eventually your souls separated and returned to their rightful places, but it didn’t change what happened. He had soul-bonded to you. He slowly removed his teeth from your mangled flesh,and the sight of all your blood on his maw was horrifying. But, again, you weren’t scared.

 

“so, uh… sorry?” he smiled nervously without meeting your eyes.


	2. Journey to the Mage City

**Summary for the Chapter:**

> alas, no smut today. we take a trip down to the mysterious underground land of mages!

“I, um, didn’t expect you to soul bond to me right away. You wanna explain that?” you crossed your arms, but that's as far as your angry facade got, still caught up in post-coital bliss.

 

He sighed. You sat next to each other in your bed, basking in the aftermath. Turns out he had moved your leftovers to the fridge and turned off the TV when he got here, but now he just stared up at the ceiling, apparently organizing his thoughts. “so… how much do you know about alternate timelines or the multiverse theory?”

 

“Enough.” he looked at you with a raised brow-bone. Weird. You had just bonded to a skeleton. You grinned back challenging. “It’s like the butterfly effect, right? One small change in the past could theoretically have created an entirely different future, or alternate timeline. And in theories like the multiverse theories, these changes did happen, and infinite universes, slightly or majorly altered, exist simultaneously in different dimensions or planes of reality.” he looked at you with a sort of amused awe. “It’s just schrodinger’s cat on a larger scale, right?”

 

He laughed outright at that. “yeah. So, i come from one of those altered timelines. I don’t how altered, since i haven’t even been here a day, but, yeah. In my timeline, you… uh…” he paused. “died.” it was barely audible, and you stiffened up. Did you want to ask? “so, i, um, kinda have this machine that can access other timelines; i’ve used it to get around and talk to a few alternate versions of myself sometimes. In my universe it’s kind of a secret, and in others only monsters know, and in some the machine doesn’t exist or work, so we can’t access those. and when i lost you, i… i couldn’t handle it. I made it a couple weeks before i was digging through my notes, experimenting with the machine, and locked it to your signature. it couldn’t take me to you, but it could find which universes i had access to where you were alive. so... i found you. I was just gonna look, see you one last time, but…”

 

“But all this happened instead.”

 

A long sigh. “yeah. Pretty much. And i have to go back, i can’t stay here. paps will miss me, and i left a lot of people without warning-”

 

“Take me with you.”

 

His eyelights flashed to hearts, but quickly reverted to the normal white dots. “You don’t mean that. This is your world, and i can’t just take you from it just because i lost my version of you.”

 

You frowned, you voice coming out louder than expected. “You just SOUL BONDED with me! You can’t just leave me like this. Anyway, i haven’t found my soulmate here, so he’ll be no worse off that you were when you… lost your version of me.” you soften your tone, laying a hand on his mandible. He instantly leaned into the touch. “Would you deny me a sure shot at being with my soulmate? My bondmate?”

 

“... no.” you sighed with relief, placing a chaste kiss to his forehead before leaning back onto the bed. You were still sore. “but getting back to the machine and going home to my universe is going to be a challenge.”

 

“Why?”

 

“well, for one, we have to go underground.”

 

You shot up to a sitting position. “Seriously?! I’ve been trying to get them to let me down there for months!”

 

Sans grinned, and the look was just… right on him. “well we can’t exactly sight-see, but we can get a couple looks at one of the areas before we go. just, uh, real quick, ‘kay? then you can explore my universe’s version as much as you like.” he seemed to be sweating  a little, which was interesting, but your mind was too caught up in fantasies of finally seeing the fabled land of exiles. He let your imagination wander as you both fell back asleep, curled up against each other in the hotel bed.

  
  
  


What a weird fucking dream. Literally. You were no stranger to some bizarre wet dreams, but why a skeleton? You had never even met a skeleton monster- oh. You turned on your side and came face-to-skull with the skeleton monster from your dream. Or, your not-dream.

 

“Holy shit,” you whispered to yourself, “i found my soulmate. We had the most amazing sex. We soul bonded. I'm going to see the underground. I’m going to travel to another world!” you rolled over in bed and screamed into a pillow. This was amazing. Just when you were worried where you would get your adrenaline kicks from if they didn’t let you meet mages, you were getting to explore an entirely new world! With your soulmate! It was basically your dream since childhood, to be an adventurer, going where no one’s ever seen before. Well, technically it’s been seen, but not by anyone in your world, and shit, what were you going to tell Rosalyn? Who cares! That’s a worry for another day. She was plenty used to not hearing from you for days.

 

“you seem pretty excited there, sweetheart,” Sans purred at you. Sans the skeleton! Your soul mate! You flung your arms around him, running fingers down his spinal column, making him growl possessively. “well, seems like somebody’s eager for another round. but unfortunately, i’m gonna need you able to walk today,” he chuckled.

 

“I can’t believe you’re going to take me underground! And to a whole other world!” you jumped out of bed, wobbling on your legs for a moment before regaining your excitement and rushing into the shower. Your body was pretty sore from your actions last night, but you pushed through it, washing away the sweat and blood and sex. Where he bit your shoulder was painful, but somehow it had already closed up and didn’t appear in danger of bleeding much more. Maybe it was a bond mark? You remember Rosalyn talking about them usually happening before a soul bond, showing that you were in a relationship, and that they healed fast initially, but not fully until your partner’s magic was out of your system or replaced. “Hey Sans?”

 

“Yeah babe?” he entered the bathroom and pushed into the shower behind you. Last night had been dark, and you were distracted from your question by your first good look at him. He was similar to a human skeleton, but his bones were fused in places, and much bigger and thicker than a human skeleton. He was a few inches taller than you, and much wider. He had a strong jaw (bone???), and you were filled with the urge to kiss it. He raised a brow bone, clean water running down his beautiful, pale frame. “see something you like?”

 

You blushed, but nodded confidently. “Yeah.” you pressed a quick kiss to his cheek before going back to cleanin yourself. “So, um, is this a bond mark?” you tapped the bite on your shoulder.

 

“oh, uh, yeah, it’s called that sometimes. like i said before, i got pretty carried away… we didn’t even have a safe word, did we? i’m really sorry about that.” he looked you over appreciatively. “well, mostly sorry anyway.”

 

You finished packing up, bringing only the necessities for your inter-dimensional trip. Or just your trip underground. It was still hard to believe he was from another timeline. Luckily, either way you were used to living out of a backpack, not really assigning value to most material things. Sure, you liked that shirt, but if you had to throw it away tomorrow you wouldn’t be devastated. And all your important files were backed up both on and offline, and if you somehow lost all that, then you’d just start over. Whatever came your way today, you could handle it.

 

You were filled with determination.

 

Sans had dressed in simple basketball shorts and a blue, fur-lined jacket, despite it being spring. As you walked through the town towards Mt. Ebott, Sans seemed incredibly interested in people-watching. He kept getting distracted by staring at the people walking by, missing chunks of conversation or even running into lamp posts and mailboxes sometimes.

 

“What,” you teased, “your world didn’t have a downtown?”

 

He chuckled, rubbing at the back of his skull. “well, monsters and humans don’t get along so well where i come from.” finally, he led you to an alley. “okay, so i’m going to take a shortcut i know, and then we’ll be under the mountain. we can look around a little, and i’ll leave you to explore while i run one last errand, but when i say go we have to go to the machine, okay?” your eager nods remind him of a puppy. He gave your hand a light squeeze and you both started walking together. 

 

It was almost seamless. You couldn’t pinpoint the exact time  the scenery changed, but suddenly the sun was gone, replaced by the warmer light of fire magic everywhere. The buildings all seemed to be made of the same gray concrete, but had various styles and intricate patterns carved into them. The people wore bright colorful clothes, and the lower floors of buildings were covered by bright posters or fabrics. But the biggest thing? There were no monsters.

 

You were underground, in the mage city.

 

Your smile threatened to stretch right off your face. “This. is so. Cool! Everything is colorful and natural and! And! It’s such a big city here!”

 

“yeah, this is the capital, new home, biggest city in the underground,” Sans said with some amount of fondness in his voice. “i’m going to go… prepare the machine, are you fine walking around on your own?”

 

“Definitely,” you responded, only paying half attention as you watched a few mages putting on some kind of performance in the square. Others had gathered around to watch and applauded as strange orbs exploded into various colors of flame.

 

“alright. If you need me, just call for me through the bond and i’ll be there in a flash. just... don’t tell anyone you’re human, okay?” you replied in the affirmative, still distracted, and he smiled down at you fondly. With a parting kiss to your forehead, he turned to leave. “I’ll be back in about an hour.” before you could tell him that an hour wasn’t nearly long enough to explore, he was gone.

 

You stepped out of the alley and into the bustling throng. It seemed that he had dropped you off near some kind of outdoor marketplace, because you could see plenty of storefronts and stalls where they sold everything from notebooks and art supplies to furniture that seemed to be made almost entirely of porous stone. Unfortunately, you were quick to note that they appeared to use a different currency than what you had on hand, so you couldn’t purchase any souvenirs. That was a bit disappointing.

 

You continued to walk around, admiring the contrast between the tall gray structures that stretched far over your heads and the bright patterns of the people around you. Honestly, you stuck out as one of the few people in a rather plain t-shirt and jean shorts.

 

“Hoi! You!” you turned to see a woman dressed in a pale blue sundress with yellow patterns stitched on, her black hair done in an… odd fashion. “Yeah! You seem like have gooood taste! Come to new shop in new home! Buy temmie flakes and other goooood products!” she held out a flyer to you, practically vibrating in excitement. Wait, no… she was actually vibrating! You cautiously took the flyer, and she jumped in excitement, throwing her arms in the air and scattering the few flyers she was holding. Except when she threw up her arms, they… kept going. They stretched several stories in the air, stopping only when another voice called out.

 

“Hey, you! No littering!” a figure in white armor came out, pointing a spear accusingly at the woman.

 

“Oops! Got too… excited! Boi!” with that she took off running down the street, arms flailing behind her and smacking into innocent pedestrians who cried out in mild alarm as the armored figure chased after them.

 

“Damn shapeshifters…” you heard several people mutter as you looked down at the flyer.

 

The flyer appeared to be several pieces of construction paper glued to a blank sheet of paper, the colorful bits spelling out “Tem Shop, buy our flakes!”. Well, that was certainly… something. You giggled, but then devolved into semi-hysterical laughter. What on earth?! The underground was certainly interesting.

  
  
  


When Sans came back, you were talking with a wizened old man. Before you noticed him, Sans took a moment to admire you. Your smile, that look of intense concentration, the need to fully absorb any new experience, your eyes… stars, it was like he never lost you. Almost reluctantly, he approached your conversation.

 

“-and so, thinking we had declared war on them, the monsters turned against us,” the old man said. “And when we went to our fellow humans with the information, they took it as an opportunity to lock us away, and also make sure the monsters could never get ahold of a mage soul. We were hunted throughout the land with the monster’s abilities to identify us, and soon we were forced under this very mountain.”

 

“That’s awful!” you exclaimed, shocked by the torture the mages had had to endure.

 

“And that’s only the half of it,” the old man nodded sadly.

 

“hey, sweetheart, we have to go,” you turned just as your soulmate took your hand. He had gloves on, and his hood hid his face. He could easily be mistaken for a human if no one looked closely. Or, in this case, a mage.

 

“Wait, can i just hear the rest of this story? Please?” you begged. This wasn’t what they had taught you in history class. And while you doubted that the mages were as innocent as this man made them out to be, you often found that the truth lay somewhere in the middle.

 

“sorry babe, but we only have a short window to get back if you wanna come with me.” meaning, Sans knew he had to get to the machine before that man got home…

 

You sadly relented and Sans almost instantly teleported you behind some building. The first thing you noticed was the cold. Wherever you were, it was freezing! Holding you tighter to his comforting warm bones, Sans opened the door with a silver key and ushered you inside the building. It was a very clean room, with a counter and a bunch of drawers, but what drew your attention was the machine.

 

Easily ten feet high, a large portion of the machine was an empty glass capsule, big enough for probaby three people to fit comfortably. The rest of it was screens, buttons, panels, and exposed wire. Some places were held together by duct tape. Sans immediately walked over to it and began fiddling with the knobs and dials, and one of the screens came on, showing a different skeleton. You couldn’t see much besides a very excited face, but even that looked very different from Sans. much more like a human skeleton.

 

“BROTHER!” the screen spoke, “IT IS READY ON THIS END. ALTHOUGH IN THE FUTURE, I WOULD APPRECIATE YOU TELLING ME WHEN YOU GO ON THESE DANGEROUS VISITS!”

 

“will do, paps. i’m sorry, this time was different. shouldn’t happen again.” Sans pressed a few more buttons, and the glass capsule opened. He motioned for you to get in, and you very carefully did. “alright, we should be there in a few seconds. see ya soon paps.”

 

“I ALSO DO NOT LIKE THAT YOU WILL NOT TELL ME WHO YOU ARE BRINGING! ESPECIALLY IF IT IS NOT THE ALTERNATE VERSIONS OF OURSELVES!” the other skeleton continued to talk, although you couldn’t see the screen from within the capsule. Sans got in beside you just as you could hear the door opening. There was a buzzing, whining sound, like something charging up.

 

“hey, skeleton?” the door to the room opened, revealing an extremely pale and stout young man. Wait, not just pale. Was he… albino? Your chest gave a strong thrum as he stepped into the room, but the whining sound was too loud to focus on much else. You saw the man reach a hand to his chest, eyes wide. You saw his visage turn angry, and it looked like he was shouting something, but then the world was black.

 

And then the world was the world. You felt extremely disoriented, like you had just gotten off of a rollercoaster that had maybe a few too many loops and twists. Up and down and sideways danced around, and as the glass capsule opened and you attempted to step out, you tripped over nothing and fell to the floor.

 

“sweetheart!” Sans called out in concern. He helped you up, but then you heard the smallest voice call out your name. 

 

You looked up and came face to chest with the skeleton from the screen. They were even taller than Sans, towering over  a foot above you, and they were lankier, thinner, as well. But what drew your attention was that he was crying. He said your name again in that quiet voice.

 

“Um, yes?” was all you could think to reply.

 

The giant skeleton quivered, and then swept you up in a tight yet gentle hug, sobbing and petting your back. “WE MISSED YOU! YOU SHOULD NOT BE HERE BUT I AM GLAD YOU ARE BUT I AM VERY UPSET AT SANS BUT IT IS SO GOOD TO SEE YOU SAFE!” well, that quiet voice was long gone. The skeleton put you down after a few spins, and then leveled a harsh gaze at a sweating Sans. “BROTHER. WHAT HAVE YOU DONE.”

**Notes for the Chapter:**

> still dont have a name for this au, tho a couple people have recommended mageswap. idk, does that sound too much like it has to do with underswap?  
> anyway, smut next chapter. enjoy, and dont forget to stay hydrated and take your meds!
> 
> help keep this THOT in college?  
> https://ko-fi.com/stripesnbooks


	3. Journey to a New World

**Summary for the Chapter:**

> well, we're in undertale now! for now.

**Notes for the Chapter:**

> yeah, its been a while since i updated this, but dont worry, i dont like leaving projects unfinished. gives me anxiety, actually. but at the end fo the chapter i got some questions for you guys! its been a while since the porn, so next chapter we'll have some more boning.
> 
> wanna help me afford groceries and stuff?  
> https://ko-fi.com/stripesnbooks
> 
> most of my posts are focused on my stories in Homes After the mountain series, but check out my tumblr for updates and stuff!  
> https://homesafterthemountain.tumblr.com/

“uuuh, well, she wanted to come here, so…”

 

Your mind was still reeling, both from the spinning and the presumably having traveled through dimensions. Papyrus’s hands were on your shoulders, firmly keeping you in place, but a look out the window showed a scenic neighborhood and a sunny day. It didn’t… look like another universe. But you were definitely no longer underground.

 

“BROTHER.” papyrus sounded displeased and exasperated. “WERE YOU NOT JUST RECENTLY TELLING ANOTHER VERSION OF MYSELF HOW IT COULD BE DANGEROUS FOR SOMEONE TO BE OUTSIDE THEIR TIMELINE FOR TOO LONG?”

 

“well, technically it’s just a theory, so we could even think of this as an experiment…” Sans was retreating into his jacket, his voice becoming more muffled and timid with every word.

 

“Um, don’t i get a say in this?” you finally spoke up, shifting experimentally to see if you could escape the grasp of Papyrus. Despite being gentle, you were still firmly trapped. “Also, could you please let me go?”

 

“OH! I DO APOLOGIZE!” he released you, and you took a few steps towards Sans. “I SUPPOSE IT IS TRUE THAT IT IS YOUR LIFE. YOU ARE NOT FRIGHTENED BY BEING BROUGHT TO ANOTHER TIMELINE? SANS HAS NOT LIED OR BAMBOOZLED YOU, HAS HE? HE DOES THAT SOMETIMES.”

 

“No, there was no… bamboozling involved. I think. But, um, Sans?” He peeked timidly at you from the fluff of his jacket. “Was that guy… that mage, was he my soulmate, too?”

 

“... yeah.”

 

Well, one of your soulmates was a mage. One of the kind that had tried to wipe out monsterkind. But then, that was centuries ago. Maybe your mage soulmate was a good person? I mean, mages were still hella dangerous, but maybe he’d be a nice one? Wait. this brought up another issue. “Sans?” your calm tone was slowly luring him out of the imagined safety of his hood fluff. “You knew that mage was my real soulmate, but you bonded with me and brought me here anyways, without telling me.”

 

Aaaaand he was back into hiding. “I’m your real soulmate too,” he whined.

 

“SANS! OH MY STARS! YOU BONDED WITH HER?! YOU WERE GONE FOR ONE NIGHT!” Papyrus was arguably taking this situation worse than you, flailing his arms wildly and sweating. “YOU SHOULD IMMEDIATELY RETURN HER AND APOLOGIZE TO EVERYONE INVOLVED!”

 

“Papyrus, wait!” you tried to get him to focus on you, and to calm down. “I don’t want to go back. I mean, i might change my mind later, but i want to stay here for now!”

 

Sans perked up a little at this. “you do?”

 

You shot him a sharp glare. “Yes, although i’ll want separate sleeping arrangements until you take me out on some proper dates. You’ve got some things to make up for, mister.” The skeleton flinched and clenched at the fabric in his chest. He could probably feel your anger and disappointment through the bond, just like you could vaguely feel his guilt and loneliness, if you focused hard on your soul. You quickly chose not to focus on your soul. “But anyway! If this is a new dimension, i wanna look around! See what’s different! Try new foods!”

 

Sans chuckled. You may be from a different timeline, but it really was still you. So excited to try something new. “well, seeing how your universe turned out, i bet you never got to try one of grillby’s burgers. I’ll take you to his place. uh, if that’s okay.” he quickly turned it into a suggestion, remembering he was on thin ice.

 

You tried to give him a cold look, but your excitement shone through too plainly. “Alright, but you’re paying!”

 

He chuckled with relief. “heh, don’t worry, i’ll put it on my tab.”

 

But then, as you turned to walk out of this… garage? The machine behind you began whirring and whining. You heard Sans utter something you recognized as a monster curse as the whining came to a deafening peak and, with a flash of light, the glass capsule was no longer empty. Instead, within stood the mage that you had seen before. His eyes locked with yours, their ice blue searching you. You felt your soul pulse with warmth and you could feel its calling even stronger than the night when Sans appeared in your hotel room. Was this because of him being your true soulmate, or did the bond with Sans strengthen your attunement to your soul? You didn’t know. This man had mid-length stark white hair tied back in a ponytail, and the ponytail swung gently as his gaze shifted from you to your skeleton bondmate. He opened the door to the capsule and stormed out. Storm being a very appropriate word, as you could practically feel the static of magic crackling around you.

 

“ _ you _ ,” the mage practically hisses as he approaches Sans, “i can’t believe you  _ kidnapped my soulmate _ !”

 

Papyrus tried to step between them and calm the situation, but instead Sans stepped up, making their height different very clear the skeleton towered over the mage by about half a foot. “i didn’t kidnap anyone, kid. she came willingly.  _ very  _ willingly.”

 

“Hey, both of you!” you pushed between them, apparently a surprise as they both stumbled back somewhat. “You are both my soulmates, so i’d prefer if you didn’t fight!” when this didn't alleviate any tension, you took a different route. “I’m the one who asked to come here! I would never have been able to even see the Underground without Sans. without him, there's no way you and i would have met,” you challenge the mage.

 

“i’m sans too,” he grumbled, but seemed to be at least somewhat calmed down. He looked at you, but seemed much less sure of himself now. “so, um, you’re my soulmate then.” he shuffled awkwardly. “nice to meet you. i’m sans but… i guess you already know that. just, wow, i didn’t even know if i had a soulmate, and then i feel the pull when you’re in the middle of a journey between dimensions, and i just…” he turns to skeleton Sans now, tone accusatory once more. “so where’s your version of her, then?”

 

The skeleton’s eyelights shrink to pinpricks, and his voice is tight. “i lost her.”

 

“oh.”

 

You want to fix this silence, but Papyrus beats you to it. “WELL! HOW ABOUT WE ALL HAVE AN EARLY DINNER AND TALK ABOUT WHAT TO DO NEXT OVER SOME FRIENDSHIP SPAGHETTI?” everyone agrees to the suggestion, and before long you are all seated at the dining table with a plate of pasta.

 

“i think it’s only fair that she bonds with me, too,” mage-sans says halfway through dinner.

 

“absolutely not,” skeleton-sans replies. “you can’t just bond with someone immediately just because they’re your soulmate.”

 

You resisted the urge to comment on that, seeing as that’s exactly what Sans did. You were instead focusing on your soul, and the very mixed signals within. It was singing for the mage-sans, you could feel it stronger than when you first met your skeleton mate yesterday. However, you could feel the emotions of skeleton-sans all too clearly through the bond, his frustration at the situation, and fear that you would be taken away, and hatred for this alternate version showing up. It was hard to keep your emotions separate, to keep from hating this human- no, mage, even as your soul longed for him. Stars, this situation was all kinds of strange.

 

“really? according to my memory, you were only in my timeline for a couple days before you did exactly that.” the mage accused.

 

The skeleton tensed. “maybe, but when i first met her in my timeline we got to know each other for a few months.”

 

“she’s not from your timeline, though. she’s from mine!” the mage’s left eye flashed yellow. “what you’ve done is wrong,  _ monster _ !”

 

“Oh, and are you guiltless,  _ mage _ ?” sans snapped back.

 

You stood up, slamming your hands down on the table next to your now empty plate. “I’m tired. I’m sleeping in your room-” you pointed to the shorter skeleton, “alone. I don’t mind having multiple bondmates but i  _ do  _ mind all this arguing about me like i’m not even here. Wake me in the morning, when you’re ready to include me in this discussion.”

 

“WELL THEN! I’LL SHOW YOU TO THE ROOM, AND THESE CHILDREN CAN TALK THINGS OUT!” Papyrus volunteered, eagerly leaving the table and putting a hand on your shoulder to gently but firmly guide you away from the other two who were both giving you pained and guilty looks. “I’M TRULY SORRY FOR MY BROTHER’S BEHAVIOR!” Papyrus said once the two of you were alone. “IT’S JUST THAT… WE THOUGHT YOU WERE DEAD AND…” his voice trailed off. “BUT OUR VERSION IS DEAD. YOU MAY BE FROM ANOTHER TIMELINE, BUT YOU AND HER ARE… DIFFERENT PEOPLE. IT WOULD BE UNFAIR TO ASK YOU TO BE THE EXACT SAME PERSON. IT WAS TRULY NOT…” he heaved a sigh. “ANYWAYS! LET ME KNOW IF YOU NEED ANYTHING, AS MY ROOM IS JUST OVER HERE. WE WILL PUT UP THE OTHER SANS IN THE GUEST ROOM, AND MY BROTHER CAN TAKE THE COUCH AND THINK ABOUT WHAT HE’S DONE.”

 

It was dark when you woke up, needing to use the restroom. You sighed, fumbling for the light switch and trying not to step on anything on your way to the door. It was with great surprised that you opened the door only to have the mage fall back into the room. He must have been sitting against the door.

 

“Oh.” what else could you say to that? “Um, hey. Sans. what are you doing here?”

**Notes for the Chapter:**

> who loves some tension? anyway, some questions for you guys.  
> 1\. what kinks do you wanna see next chapter?  
> 2\. any ideas for a nickname for mage sans? we haven't seen much of his personality yet, so its okay if you dont have anything.
> 
> my laptop is kind of broken, so really. if you can spare anything.  
> https://ko-fi.com/stripesnbooks
> 
> come ask me questions! ask mage!sans questions! ask yourself questions. question everything.  
> https://homesafterthemountain.tumblr.com/


	4. Journey to More Complications

**Notes for the Chapter:**

> wow. its here after one million years. i originally planned a series of small adventures with lotsa smut as the focus, but also plot and universe-hopping. i dont know if i still wanna do it, but if enough people wanna see it i might try.
> 
> but yeah, here you go! 
> 
> contains: sex, minor bondage, maybe an angery skele?

“sorry, i, uh,” the Mage quickly got up and brushed himself off. “had a nightmare, and, well… beingnearyoucalmedmysouldown.”

 

You calmed… his soul? With this information, you could practically hear your soul hum. Before falling asleep, you had been kept awake by your bondmate’s anxiety and regret, but he must be asleep now, since it had calmed down. You could still feel skeleton Sans through the bond, but it was peaceful, unintrusive. “I’m… sorry you had a nightmare. Do you want to come in?” wait wait wait why were you inviting him inside this is a terrible idea-

 

“...yeah. yeah. i’d really like that.” he gave you a soft smile and you could feel your breath catch at how beautiful he was when he smiled.

 

“I’ll be right back!” you quickly ran to use the restroom, and soon found yourself washing up, looking into the mirror. On your shoulder was the mark of Sans’s teeth on you, from the night you had bonded. Last night. But now your soul called out for another, so soon… soulmates were complicated, sure, but you hadn’t been prepared for them being  _ this  _ complicated! And the worst part was: you were enjoying it. The intrigue, the adventure, having multiple people want you… despite the mess, it made you feel  _ good _ . Alive. Excited. And you didn’t know if that was healthy. Returning to your room, you found the mage Sans sitting on your bed, fiddling with his hands and staring off into space.

 

“Sans?”

 

His gaze shot to you immediately, and he gave a half hearted grin. “hey. safe trip?”

 

You rolled your eyes. “The journey to the bathroom was a harrowing one, with the danger of creaking floorboards around every corner.” sitting down on the bed near him, you found yourself drawn to his eyes again. His face had a round nose, thick lips, that incredibly pale skin… and his eyes were ice blue. You had thought people with albinism had red eyes, since albino animals usually did, but apparently not. Or was that rude? Was it rude to think that?

 

“take a picture sweetheart, it’ll last longer,” he said with a grin. You quickly looked away, a bit embarrassed you had been caught staring. His smile softened. “look, i wanna… apologize for earlier. talking about you like you were a thing rather than a person. it wasn’t right. i’m sorry.” now he looked away from you, staring off at nothing again.

 

You didn’t like it, him feeling bad. Even though he really deserved to. But he had apologized, so it was okay, right? You reached a hand over to lay on top of his. Flesh on flesh. “... i forgive you.”

 

His head jerked around, hope in his eyes. “r-really?” 

 

“Yeah, really.”

 

You found yourself caught up in a warm hug, with the mage’s face buried into your shoulder. “thank you…”

 

Almost out of your control, your arms wrapped around him in a tight squeeze. “it's… it's fine, everyone was upset and stuff.”

 

“yeah... still…” he slowly and reluctantly pulled away. “guess i’d… better get back to my room.”

 

“You don’t have to.” what were you saying now?! Why did you feel for them so strongly, so quickly?! This was ridiculous! But you didn’t want him to go back. You wanted to be near him. This was ridiculous. It didn’t make any logical sense. But. it  _ was  _ exciting, this feeling. “You can stay with me tonight, if you want.” and he seemed so… lonely. His face didn’t say it, even the tone of his words was only sad, but something  _ called  _ to you that he was lonely… and he needed you.

 

“... are you sure?” he asked, looking at you nervously, but also very seriously.

 

“Yes.” you patted the bed next to you. “No more nightmares.”

 

There was a tightness to his steps as he slowly moved back to the bed, as if you would run away at any moment. But you didn't, and he slid down to sit on the very edge of the bed, eyes trained on you. You scooted over to make more room.

 

“It’s okay, I don’t bite,” you said with a cheeky grin.

 

He flashed you one right back as he fully laid down in the bed, pulling up the covers before turning away. “... thanks. really. i’ll try and stay on this side.”

 

You fell asleep almost immediately, and you had to wonder if it was because your soul mate was next to you- well, one of your soul mates. How well would you sleep with both, you wondered? You didn’t wake up for a good while, and when you did, the mage was on top of you, holding you close and making his morning wood very obvious. You couldn’t help but let out a snort from that, giggling softly. He groaned, shifting atop you and grinding against you, making heat shoot unbidden to your core. You… kind of wanted to help him with that. Would that be unfair to skeleton Sans? Stars, these guys needed nicknames. But the monster hadn’t really apologized to you, while the mage had. And the mage was also your soulmate, and in your bed, and in need of… help. You angled yourself a bit before grinding against him. He let out another groan as his eyes flickered open, widening when he realized where he was and what you were doing.

 

“uh, good morning?” he said hesitantly.

 

You smiled at him. “Morning, sunshine. Sleep well?” you gave another grind against him, relishing in the way his eyes widened and his breath caught.

 

“y-yeah. so, uh, you seem…” he seemed to struggle to find a word more delicate than ‘horny’, “...eager.”

 

You laughed. “I just couldn’t help but notice you had a… problem that i might be able to help with.”

 

He stared at you intensely, searching your face for something. “i mean… i’d like that, but…” you ground against him again and he growled, grabbing your hips and holding them down. “let me finish. you sure you wanna do this?”

 

You looked up, confused. “Of course. You’re my soulmate. I trust you.” 

 

“thats… fuck it.” he threw the blanket back and let go of you to free his erection from his shorts, and you quickly pulled off your own underwear. He snatched it from your hands, and somehow twisted it to bind your hands together above your head. “... you ready? i’m not sure if i'll be able to stop once i start.”

 

You stared at his girthy member, licked your lips, and gave a nod. “I… I want this.”

 

His left eye seemed to flash gold for a moment as he growled at your statement. His fingers wandered down, easily finding your soaked pussy, and he guided his dick into your folds. You moaned as he filled you, stretching your walls wonderfully, if a bit painfully. He hadn't prepped you at all, and so it burned a bit when he started to move. But it felt good. You liked it. And as he moved faster, thrusting into you, your walls quickly grew accustomed to his size. 

 

“...nng… fuck…” he hissed through clenched teeth, one hand pinning your wrists above your head as he used the other to support himself above you. “you feel… so stars damned good…” you moaned louder as he angled himself to hit your g-spot, pounding into it over and over. 

 

“S-sans, fuck… more, please…”

 

He seemed all too happy to oblige, going faster. “you… are mine… no one else's… my soul mate…” it wasn't true, and he had to know that, but you let him have it. In this moment, you were his alone, and he was yours. His grip on your wrists tightened as he drove himself into you deeper and deeper, and you felt your walls flutter. 

 

“Close…” you practically begged, dying to be pushed over that edge. 

 

He slowed down, focusing more on force than speed, that lovely friction within you assuming to intensify as with another hard thrust, your walls clamped down around him. You cried out, and he sped up again in search of his own end, finally spilling his seed into you, more and more, until it started leaking out from between you as he finally slowed. He slumped over you, petting your hair. “... thank you,” he whispered almost reverently. In response you just kissed him. 

  
  
  


A few rooms over, a certain skeleton ground his teeth in anger, clutching at his chest where his soul lay beneath his jacket. He had woken up to the feeling of his soulmate… being played by someone else. And he wasn't happy about it. 

**Notes for the Chapter:**

> so yeah, hope you had fun!
> 
> be sure to drop by my tumblr:  
> https://homesafterthemountain.tumblr.com/  
> and i try to also put links to fics on my twitter:  
> @stripesnbooks
> 
> if you can, theres a ko-fi link on my tumblr! i dont currently have a stable source of income, so consider giving that a look-see.

**Author's Note:**

> So, no idea how often this will update, but it'll eventually be an AU hopping series. its gonna keep being mostly porn tho, fair warning.  
> future chapters may ask for your input on what aus you wanna see, what kinks you like, ect, maybe if it get popular i'll do a raffle or something, idk. we'll see.
> 
> keep this THOT in college?  
> https://ko-fi.com/stripesnbooks


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